Typically liquid filtration and in particular water filtration is needed for the omission of pollutants and other unwanted materials. Membrane filtration systems are used to filter liquids and typically include a set of filtering elements made of porous membranes within a module or cell. The use of membranes is a well-known and effective separation process. Different membrane types, including nano-filtration (NF), ultra-filtration (UF), micro-filtration (MF) and reverse osmosis (RO), are used to remove suspended particles, colloids, microorganisms and even reject ions in solution1.
In operation, pollutants in a fluid gradually form a cake layer on surfaces of the porous membrane and/or block the pores of the porous membrane2. To maintain satisfactory filtration performance, it is necessary to restore the membrane performance after a certain filtration time by replacement of the filter or cleaning of the filter membrane.
There are several methods to restore membrane performance. One method of restoration involves replacing all the membranes when an increasing amount of pressure, called head loss, has exceeded a specified value3. This method has certain disadvantages, such as the handling of a large volume of the impurities retained by the membranes and handling of these replaced membranes themselves. Additionally, membrane replacement leads to increased labor work and cost as well as increased time of suspension of the filtration system.
Another restoration process is backwashing, which consumes a certain quantity of clean water to pass in countercurrent through the filtering membranes. While the backwashing method avoids the demounting of the filter and the replacement of the membranes, backwashing is not ideal because a large volume of clean water is required for cleaning. This results in a large amount of contaminated wash water requiring proper disposal or treatment. Additionally, backwashing requires suspension of filtration operation and therefore interrupts the continuous filtration process.
Chemical cleaning is another restoration process, which involves the use of corrosive acid or base solution, oxidants, or detergents to clean fouled membranes4. Accordingly, membrane degradation may be a problem due to the harsh chemicals5, and requires suspension of the continuous filtration process. For example, while some chemicals, such as oxidant and caustic soda, will chemically oxidize and remove surface foulants, these chemicals may damage the membrane integrity and shorten the lifetime of membranes, especially polymer membranes. Additionally, this process results in more chemical consumption and higher waste handling and disposal cost.
Another process to restore membranes involves the use of external field forces to aid filtration. For example, magnetically assisted filters6, electrically assisted filters7, and ultrasonically enhanced filtration8 are proposed to mitigate membrane fouling. However, these methods suffer high-energy consumption, membrane erosion, and non-uniform energy distribution on the fouled membrane surface.
Accordingly, there is a pressing need in the membrane filtration industry to develop an anti-fouling filtration system without interrupting the filtration process and with a uniform distribution of energy to save operation costs.
Thus there still remains a need in the art for an anti-fouling system without the above drawbacks. Furthermore there also remains a need in the art for a filtration system that eliminates the need to replace the filter membrane and does not include the above drawbacks of restoring the membrane as seen in the current systems.